v1.3.0

• Clean up some duplicate members when targeting .NET Standard:
  • Async extension methods for Ping, SmtpClient, Stream, WebClient, WebRequest
  • CompletedTask static class
• Use nameof() when passing argument names to ArgumentOutOfRangeException and ArgumentNullException
• XML documentation improvements:
  • Don't hardcode true, false, null, and other language specific keywords
  • Use <see> and <paramref> when referring to members/parameters where it makes sense
  • Fix a few typos